Internet retail titan Amazon on Thursday introduced a home virtual assistant always at the ready to answer questions, fetch news, play music or help with to-do lists.

Internet retail titan Amazon on Thursday introduced a home virtual assistant always at the ready to answer questions, fetch news, play music or help with to-do lists.

The cloud-based brains referred to as "Alexa" are built into Echo speakers and seen as a challenge to "Siri" virtual assistants in Apple's coveted mobile devices.

Echo became available on an invitation-only basis at a price of $199, or $99 for those who pay for the Seattle-based company's Prime subscription service.

"Echo's brain is in the cloud, running on Amazon Web Services so it continually learns and adds more functionality over time," Amazon said at a web page where people could request invitations to buy the Bluetooth-enabled speakers.

"The more you use Echo, the more it adapts to your speech patterns, vocabulary, and personal preferences."

A demonstration video online revealed a female voice responding to questions or commands preceded by the trigger word "Alexa."

A ring of microphones built into can-shaped Echo speakers enable the devices to identify voices even when music is playing, according to Amazon.

Echo accesses news, weather, streaming music and more using wireless Internet connections.

Echo can also be managed remotely using free applications built for smartphones powered by Apple, Android or Amazon's Fire operating software.

Making homes 'smart'

Internet titans such as Apple and Google are eager to make their platforms hubs that exploit powers of smartphones, tablets or other devices to serve as controls for entertainment, information, temperature, lighting, and more in "smart homes," according to Forrester analyst James McQuivey.

Echo could let Amazon jump ahead in that race with the first device in homes that will be listening and ready to act whenever people might think of something they want or need to buy.

"Sure, it doubles as a connected speaker and some people will end up buying it for that, but the Echo will only achieve its real purpose when you start asking it questions, having it complete tasks for you -- especially shopping tasks -- just the way Apple hopes its users will interact with Apple Watch," McQuivey said.

"Amazon has a unique ability to monetize the microphone, principally by putting microphones in places where you will think of things you want to buy -- the kitchen, the bathroom, the living room -- things which Amazon can then easily fulfill."

The debut of the Echo likely caught rivals off guard, especially with Amazon still stinging from the lack of consumer interest in a Fire smartphone it recently released to compete in that market, according to the analyst.